In electrical equipment with conductors cooled to low temperature, it is often necessary to supply the electric current to the cooled conductors from a power supply at ambient temperature. This applies in particular to superconducting cables, the superconductors of which must be cooled down to a temperature below the transition temperature of the superconducting material.
A superconducting cable is known from EP 1 363 062 A1, which passes through a so-called cryostat. The cryostat consists of two concentric, corrugated metal pipes. Between the corrugated metal pipes is a blanket of so-called superinsulation consisting of alternating layers of metal foil and cold-resistant plastic film, e.g., film based on polyester. The film obtainable commercially under the trade name “Mylar” is preferred. Mylar is a registered trademark of Du Pont de Nemours. The annular gap between the metal pipes is also evacuated.
With respect to the current supply, care must be taken to ensure that the high voltage-carrying conductor of the power supply is isolated from the cryostat, which is at standard potential. It is also necessary for the vacuum present in the annular gap to be sealed off against the interior of the cryostat.